1. Field of the Invention
This invention relates to synthetic monofilament twines. More particularly, this invention relates to synthetic monofilament twines produced from a bundle of orientated thermoplastic monofilaments which are twisted along the length of the twine and which are bound by a thermoplastic material which extends around the bundle in a spiral form.
2. Prior Art
U.S. Pat. No. 2,552,210 to W. B. Parker discloses a ply yarn comprising a bundle of natural fibers entwined together with a fine filament nylon yarn. The ply yarn has a twist imparted to it.
U.S. Pat. No. 3,315,454 to Enerza discloses a synthetic twine suitable for forming knots in baling, tying and other automatic knot tying machines. The twine comprises a plurality of filaments of a thermoplastic resin and containing dispersed therein a gas so as to produce foamed filaments.
U.S. Pat. No. 3,446,002 to Kippan discloses a twine comprised of a bundle of substantially parallel synthetic monofilaments with a synthetic binder material in thin band form wrapped around and fused to the outer monofilaments.
U.S. Pat. No. 3,577,873 discloses a core yarn comprising a core component of set false twisted synthetic continuous multifilaments and at least one wrapping component of synthetic continuous filaments formed in helices around the core components, the direction of the helices being reversed at intervals along the yarn.
U.S. Pat. No. 3,769,787 to Rosenstein et al discloses a multiple filament yarn of a synthetic textile useful for knitting, winding and weaving which multi-filament textile yarn has continuously disposed thereabout two special wrapper filaments wrapped in a generally helical path about the core filaments of the yarn, one wrapper being disposed in a clockwise manner and the other wrapper being disposed in a counterclockwise manner.
U.S. Pat. No. 3,851,457 to Waters discloses a core yarn comprised of a set false twisted core and a wrapper of filaments formed in reversing helices.
Kippan in U.S. Pat. No. 3,415,919 notes several disadvantages of the twisted twine. The primary disadvantage is a weaker twine, since the helices are able to assume only a portion of an applied tensile load, whereas in a parallel alignment of monofilaments as disclosed in his patent, each filament is able to fully bear an applied tensile load. In theory, at least the tensile strength of a twine having all of the monofilaments aligned is the sum of the tensile strength of each filament (in practice tensile strength is slightly less).
It has been found nevertheless that the twine or cord such as described by Kippan having parallel monofilaments bound by an extruded binder presents certain disadvantages when employed in mechanical balers. The straight monofilaments can be deformed in a knotting operation such that the individual fibers break out between the spiral binding. The structure becomes less homogeneous in the knotting step and a protruding monofilament may catch in the mechanism. Furthermore, the tensile strength of the twine involved in the knot is considerably reduced over the tensile strength of the linear twine.